JPH0552673A - Optical fiber type temperature distribution measurement device - Google Patents

Abstract

PURPOSE:To measure temperature distribution at high accuracy through an optical fiber type temperature distribution measurement device by extracting induced Raman light effectively. CONSTITUTION:Induced Raman scattering is generated by injecting an optical pulse generated by a LD excitation solid state laser 11 into an optical fiber 13, in an optical fiber type temperature distribution measurement device. A component of desired wavelength of the induced Raman light thus generated is extracted from a light filter 4, and is injected into an optical fiber 9 to be measured, and the Raman scattering light ejected from the other end is detected, signal-processed, so as to measure the temperature distribution in the optical fiber to be measured. As the optical fiber 13, distributed shift single mode fiber is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects Raman backscattered light when pulsed light is incident on one end of an optical fiber, and detects the Raman backscattered light at each position along the length of the optical fiber from the value of the light intensity at each time. The present invention relates to an optical fiber type temperature distribution measuring device for measuring temperature, and particularly to an optical fiber type temperature distribution measuring device capable of highly accurate temperature distribution measurement.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing the configuration of a conventional optical fiber type temperature distribution measuring apparatus. A fiber Raman laser unit 1 including an LD pumped solid laser 11 and an optical fiber 12 is used as a light source, and pulsed light generated from the laser Raman laser unit 1 passes through an optical attenuator 2, an optical filter 4, and a spectroscopic device 3, and then an optical fiber 9 to be measured Is incident on. Spectroscopic device 3
Is composed of, for example, a diffraction grating or an optical filter film using a derivative multilayer film. The wavelength component of the Raman backscattered light generated in the measured optical fiber 9 is separated by this spectroscopic device 3. Then, the light of the two wavelength components of the Stokes light and the anti-Stokes light separated by the spectroscopic device 3 is
It is sent to the digital averaging circuit 7 via the light receiving element 5 and the amplifier 6, respectively. The digital averaging circuit 7 is connected to the computer 8 and exchanges data with each other.

In the digital averaging circuit 7, the input signal is sampled and A / D converted from the trigger signal sent to the LD pumped solid-state laser 11 as a starting point to generate data on the intensity of the backscattered light. , S / N ratio is obtained by adding data obtained when the pulsed light is incident on the optical fiber 9 to be measured for each unit time, and further adding data when the pulsed light is repeatedly incident, to obtain the S / N ratio. I am trying to raise it. The data thus obtained is sent to the computer 8 and, for example, by displaying the horizontal axis as the data sampling time and the vertical axis as the data size,
The measured temperature at the position in the length direction of the optical fiber 9 to be measured is represented.

Optical fiber 1 of fiber Raman laser unit 1
A high-output pulsed light having a size equal to or larger than a threshold value at which stimulated Raman scattering is generated is input to 2. Therefore, pulsed light with a high output of several W or more is required. Therefore, the LD pumped solid-state laser 11 is used to obtain pulsed light with a wavelength of 1.321 μm. Generally, when light is incident on an optical fiber, Rayleigh scattered light of the same wavelength as the incident wavelength and Raman scattered light of which the wavelength is shifted are generated, and the scattered light intensity increases in proportion to the incident light intensity. A nonlinear effect occurs when the threshold value is exceeded, and the Raman scattered light intensity increases rapidly. And the Stokes light of higher order, which was too weak to observe in the linear region, becomes large. On the contrary, the Rayleigh light and the anti-Stokes light are deprived of energy by the Stokes light, and the intensity is significantly reduced.

The stimulated Raman scattered light is generated as first-order, second-order, third-order, ..., Higher-order Stokes light on the wavelength side longer than the incident light wavelength. The wavelength of incident light is 1.321 as described above.
and the wavelengths of the first, second, third, and fourth Stokes light are 1.403 μm, 1.495 μm, 1.
It becomes 600 μm and 1.721 μm. This stimulated Raman scattered light has high intensity, and light with an intensity of several hundred mW or more necessary for observing the Raman backscattered light can be obtained in a wide wavelength range.

In the pulsed light emitted from the optical fiber 12 in this way, only the wavelength (1.403 μm) component of the first-order Stokes light is extracted by the optical filter 4, and the emission wavelength component of the LD pumped solid state laser 11 and stimulated Raman scattering are generated. Rayleigh scattered light generated in the optical fiber 12, second order, third order,
The wavelength components of fourth-order, ..., Higher-order Stokes light are cut. The intensity thereof is adjusted by the optical attenuator 2 so that the intensity thereof is equal to or smaller than the threshold value that causes stimulated Raman scattering in the optical fiber 9 to be measured.

The measured optical fiber 9 has a wavelength of 1.403.
Raman scattering occurs when pulsed light of μm is incident, and Stokes light of wavelength 1.495 μm and wavelength 1.
The 321 μm anti-Stokes light returns to the incident end side as backscattered light, and the light of these wavelength components is separated by the spectroscopic device 3.

[0008]

By the way, in the above-mentioned conventional optical fiber type temperature distribution measuring device,
Since the 03 μm stimulated Raman light could not be extracted efficiently, the accuracy of temperature distribution measurement was extremely limited. That is, as can be seen from the stimulated Raman scattered light spectrum shown in FIG. 3, the single mode fiber 12 used in the conventional fiber Raman laser section 1 can extract a certain amount of output in a wide wavelength range, but the wavelength 1 ．
This is because the light intensity of 403 μm cannot be increased.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to efficiently extract stimulated Raman light as a light source used for a temperature sensor, and thereby to perform temperature distribution measurement with high accuracy. An object is to provide a distribution measuring device.

[0010]

In order to achieve the above object, the present invention provides an LD-pumped solid-state laser that generates high-power pulsed light, and an optical fiber that causes stimulated Raman scattering when the pulsed light is incident on one end. And an optical filter for extracting a desired wavelength component from the stimulated Raman scattered light emitted from the other end of the optical fiber, and an output light of this optical filter is incident on one end of the optical fiber to be measured and emitted from one end thereof. Optical means for taking out the Raman backscattered light of the measurement optical fiber, a light receiving element for converting the taken Raman backscattered light into an electric signal, and a digital averaging circuit for A / D converting the electric signal to perform averaging processing. In the optical fiber type temperature distribution measuring device including the above, a dispersion shift single mode fiber is used as the optical fiber.

[0011]

According to the above construction, when the dispersion-shifted single mode fiber is used as the optical fiber, when the pulsed light having the wavelength of 1.32 μm is incident, the stimulated Raman light having the wavelength of 1.40 μm with high light intensity can be efficiently obtained. You can take it out. Therefore, by using the stimulated Raman light of high light intensity as the light source, it is possible to measure the temperature distribution with high accuracy.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an optical fiber type temperature distribution measuring apparatus which is an embodiment of the present invention. The difference between this embodiment and the conventional circuit shown in FIG.
The fiber Raman laser unit 1 using the single mode fiber 12 is replaced with a fiber Raman laser unit 1A using a dispersion shift single mode fiber 13.

When strong light is incident on either the single mode fiber 12 or the dispersion shifted single mode fiber 13, it shifts to stimulated Raman, but the primary Stokes light is not observed on the single mode fiber 12 as shown in FIG. On the other hand, dispersion-shifted single-mode fiber 1
In Example 3, when pulsed light with a wavelength of 1.32 μm is incident, as shown in FIG. 2, primary Stokes light with high light intensity centered at a wavelength of 1.40 μm is observed. By taking out the primary Stokes light of high light intensity by the wavelength filter 4 and using this light as a light source, it is possible to measure the temperature distribution with high accuracy.

In this embodiment, the dispersion-shifted single-mode fiber 13 having a zero-dispersion wavelength that does not match the wavelength of the source light is selected and its total length is set to 50 m. The reason for this will be described below. When a certain intensity of light is incident on the dispersion shift single mode fiber 13, the intensity of the primary Stokes light changes depending on the length of the fiber. In this case, the total length is 10m, 20
When m, ..., 50 m is changed, the intensity of the first-order Stokes light gradually increases, and when it is further increased, higher-order Stokes light is generated and it becomes difficult to use as a stimulated Raman light source. Therefore, 50 m is the optimum length.

Even when the length of the dispersion-shifted single-mode fiber 12 is fixed and the intensity of light incident on the fiber is increased, the intensity of the primary Stokes light is increased accordingly, so that an appropriate optical output is obtained. , And a dispersion-shifted single-mode fiber with an appropriate length accordingly. In this case, in order to make it compact, a light source having a high output may be used and a short dispersion shift single mode fiber may be used.

[0016]

As described above, according to the optical fiber type temperature distribution measuring apparatus of the present invention, the dispersion-shifted single mode fiber is used as the optical fiber for injecting the high-power pulsed light to cause stimulated Raman scattering. Therefore, the wavelength 1.
When the pulsed light of 32 μm is incident, the stimulated Raman light having a high light intensity and a wavelength of 1.40 μm can be efficiently extracted, and this has the effect of enabling highly accurate temperature distribution measurement.

[0017]

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical fiber type temperature distribution measuring device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a stimulated Raman scattered light spectrum of a dispersion shifted single mode fiber used in an example of the present invention.

FIG. 3 is a waveform diagram showing a stimulated Raman scattered light spectrum of a single mode fiber used in a conventional optical fiber type temperature distribution measuring device.

FIG. 4 is a block diagram showing a configuration of a conventional optical fiber type temperature distribution measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fiber Raman laser section 3 Spectroscopic device (optical means) 4 Optical filter 5 Light receiving element (light receiving element) 7 Averaging processing section (digital averaging circuit) 11 LD pumped solid state laser 13 Dispersion shift single mode fiber (optical fiber)

Claims (1)

[Claims] 1. An LD-pumped solid-state laser that generates high-power pulsed light, an optical fiber that causes stimulated Raman scattering when the pulsed light is incident on one end, and stimulated Raman scattering that exits from the other end of the optical fiber. An optical filter for extracting a desired wavelength component from the light, and an optical means for extracting the Raman backscattered light of the measured optical fiber which is incident on one end of the measured optical fiber and is emitted from the one end of the output light of this optical filter, In the optical fiber type temperature distribution measuring device comprising a light receiving element for converting the extracted Raman backscattered light into an electric signal, and a digital averaging circuit for averaging the electric signal by A / D conversion, An optical fiber temperature distribution measuring device characterized by using a dispersion-shifted single-mode fiber as the fiber.